# Integral Field Spectroscopy of the Low-Mass Companion HD984B with the Gemini Planet Imager

## TL;DR

This paper reports detailed observations and orbit fitting of the low-mass companion HD 984 B using the Gemini Planet Imager, revealing its spectral type, temperature, luminosity, and mass estimates, and introduces a spectral analysis method.

## Contribution

It presents the first orbit determination of HD 984 B and a novel spectral covariance analysis method for better spectral characterization.

## Key findings

- Orbit of HD 984 B is approximately 18 AU with a 70-year period.
- Spectral type of the companion is M6.5+/-1.5 with a temperature of about 2730 K.
- Mass estimates range from 34 to 95 Jupiter masses depending on age.

## Abstract

We present new observations of the low-mass companion to HD 984 taken with the Gemini Planet Imager as a part of the Gemini Planet Imager Exoplanet Survey campaign. Images of HD 984 B were obtained in the J (1.12--1.3 micron) and H (1.50--1.80 micron) bands. Combined with archival epochs from 2012 and 2014, we fit the first orbit to the companion to find an 18 AU (70 year) orbit with a 68% confidence interval between 14 and 28 AU, an eccentricity of 0.18 with a 68% confidence interval between 0.05 and 0.47, and an inclination of 119 degrees with a 68% confidence interval between 114 degrees and 125 degrees. To address considerable spectral covariance in both spectra, we present a method of splitting the spectra into low and high frequencies to analyze the spectral structure at different spatial frequencies with the proper spectral noise correlation. Using the split spectra, we compare to known spectral types using field brown dwarf and low-mass star spectra and find a best fit match of a field gravity M6.5+/-1.5 spectral type with a corresponding temperature of 2730+120 K. Photometry of the companion yields a luminosity of log(L_bol/L_sun) = -2.88+/-0.07 dex, using DUSTY models. Mass estimates, again from DUSTY models, find an age-dependent mass of 34+/-1 to 95+/-4 M_Jup. These results are consistent with previous measurements of the object.